Remote laser delivery systems involve the delivery of light energy through a fiber optic cable and directing the light energy to a target surface to produce visual effects, heating or prolonged light exposure. UV photolithography, welding, engraving, sensors and analytical instruments are among the uses for remote laser delivery systems. In addition, the medical sciences have been advanced through the use of remote laser delivery systems to perform precise cutting and ablation of tissue in surgery, as well as, photodynamic non-ablative therapy such as hair removal, topical laser peel.
Maximizing the energy transmission capacity and maximizing the service life of a fiber optic cable are important concerns in designing remote laser delivery systems. Maximizing the number of distinct physical paths in which light energy travels in a conduit provides for maximized energy delivery capacity of the conduit. Accordingly, the energy transmission capacity of a fiber optic cable is increased by filling all available modes through which light energy (photons) propagate. The useful life of a fiber optic cable tends to be decreased when the light energy is concentrated in a relatively few modes due to localized heating of the fiber optic cable. It is common for the photons launched into a fiber optic cable to initially fill relatively few modes resulting in irregular photon density in the planes traverse to the direction the photons travel. Redistribution of the light energy to fill additional available modes results in a more uniform energy distribution and maximizes the service life of the fiber optic cable.
In addition to maximally filling the available fiber modes, reducing or eliminating cladding modes is important to preventing premature failure of a fiber optic cable. The fiber cladding is not intended as an energy conduit and removal of photon energy trapped within the cladding of the fiber can extend the service life of a fiber optic cable.
One method of redistributing light energy in a fiber optic cable is with a mode scrambler that introduces physical bends in the fiber optic cable. The trajectories (paths) of photons are altered by the physical bends to cause more modes to be filled. Prior art methods of introducing physical bends are problematic for fiber optic cables rated for high energy delivery due to the typically large cable diameter and corresponding increased resistant to mechanical bending. Also, the core of a fiber optic cable rated for high energy delivery are often composed of a silica glass, rather than plastic, which is comparatively stiff, having high tensile strength and high modulus of elasticity.
Many early advances in mode scrambler technology were driven by communication applications. However, design considerations involved in designing remote laser delivery systems differ substantially from fiber optic communication systems. In communication systems, light signal modulation and detection rather than energy delivery is the primary concern. Fiber optic cables utilized for communication commonly have a bend radius measured in inches. Whereas, fiber optic cables used for high-energy deliver may have a minimum bend radius that is measured in feet. Likewise, optimal mode filling is generally less important in communication systems than in high-energy delivery systems. New methods are needed to provide more effective fiber optic mode scramblers suitable for remote laser delivery systems, which maximize the energy capacity and life of a fiber optic cable and conserve physical space.